Thermal inkjet printers apply ink to a print medium by ejecting small droplets of ink from an array of nozzles located in a printhead of a print cartridge. An array of thin-film resistors on an integrated circuit on the printhead selectively generates heat as current is passed through the resistors. The heat causes ink contained within an ink reservoir adjacent to the resistors to boil and be ejected from the array of nozzles associated with the resistor array. A printer controller determines which resistors will be "fired" and the proper firing sequence so that the desired pattern of dots is printed on the medium to form an image.
Typically, replaceable printhead cartridges include integrated ink reservoirs. Due to weight limitations, these reservoirs usually contain much less ink than the printhead is capable of ejecting over its intrinsic lifetime. The useful lifetime of a printhead cartridge can be extended significantly if the integrated ink reservoir can be refilled. Several methods now exist for supplying additional ink to the printhead after the initial supply in the integrated reservoir has been depleted. Most of these methods involve continuous or intermittent siphoning or pumping of ink from a remote ink source to the print cartridge. The remote ink source is typically housed in a replaceable ink cartridge which is "off-carrier", meaning it is not mounted on the carriage which moves the printhead cartridge across the print medium. The ink usually travels from the remote ink cartridge to the printhead cartridge through a flexible conduit.
One problem associated with refillable printhead cartridges is the possibility of refilling the cartridge with ink of a color that does not match the color of the original ink. Mismatched ink colors can lead to unfortunate results, especially when the cartridge refill occurs during an ongoing multicolor printing task. Mismatched ink formulations, such as dye-based ink mixed with pigment-based ink, can also lead to undesirable results.
Such problems have been addressed in the past by provision of mechanical features to force compatibility between the printhead cartridge and the off-carrier ink cartridge. Such mechanical features have been added to the printhead cartridge, the off-carrier ink cartridge, or both. However, as the number of ink colors and special ink formulations increase, mechanical systems become inadequate to provide for all possible combinations. Therefore, a means of assuring compatible combinations of printhead cartridges and remote ink cartridges is needed.